NNTO means "no need to open," while EOM means "end of message."
If you just need to send a quick, casual update to your team or a connection, Leonov said this tag is a great addition to a email subject line. Just write what's important in the subject and leave it at that.
Some workplaces might prefer to send this sort of note over a messaging app, like Slack, instead of fill up people's inboxes. But if your workplace is email-reliant, this might be a useful tip for you.